The efficiency of flotation of sulfide minerals is controlled by a number of variables, one of which is the particle size and configuration of the material being floated. In general, the greater the quantity of slime bearing constituents, the poorer the separation of minerals in gangue. In most primary copper deposits, the naturally occurring slimes and that produced by beneficiation are of sufficient quantity to detrimentally affect overall flotation recoveries.
Attempts to avoid slime formation have included efforts to eliminate fine grinding. As an example, some mill feed are ground to run roughly 50% minus 200 mesh and 40% minus 325 mesh. Such a grind is necessary for optimum liberation of the desired minerals. If not ground fine enough, slime formation may be avoided, but the recovery of the desired mineral is low. This grind range does not, however, indicate the true slime content of the material. The primary slimes or slimes not produced by beneficiation tend to have a greater affect on flotation. In order words, the particle size distribution below the -325 range and particularly the fractions approaching the micron range are the controlling factors. These slimes vary with the mining areas to such a degree that various areas allow extremely poor physical control of the flotation operation.
Addition of chemicals to suppress the detrimental effect of slimes has been tried with some minor success, but such chemicals do not sufficiently improve the grade of rougher concentrates so as to permit a more efficient cleaner flotation circuit.